1. Field of the Invention
The present invention relates to arc resistant cabinets for electrical equipment. More specifically, the invention relates to an exhaust chamber for such a cabinet, adapted to channel high temperature expanding gases away from personnel.
2. Description of the Related Art
Electrical equipment such as circuit breakers are typically contained within arc electrically grounded resistant cabinets, intended to provide isolation for the components therein, and to protect personnel working around the circuit breaker from electrocution and from hot gases in the event of an electrical arc within the cabinet. Such an electrical arc would cause a sudden pressure increase inside the cabinet and localized overheating.
Presently available arc resistant cabinets typically include a frame having a hinged flap assembly. Such flaps are designed to support the weight of personnel working on top of the cabinet, but to open to relieve pressure inside the cabinet when an arc occurs. However, such gases may be deflected off the ceiling and wall of the room wherein the cabinet is located, down on to personnel working near the cabinet. Current and proposed safety standards require that the temperature of such gases be tested by placing highly flammable cotton indicators at a height of 2 meters around the perimeter of the cabinet, and these cotton indicators must not ignite when an internal arc occurs.
Accordingly, there is a need for an arc resistant cabinet having a means for directing high temperature, expanding gases exiting the cabinet away from locations where personnel are likely to be present. Additionally, there is a need for an arc resistant cabinet having a means for relieving pressure from high temperature, expanding gases while being easier and less expensive to produce than other arc resistant cabinets.
The preferred embodiments of the present invention are exhaust chambers for use with arc resistant cabinets. Such exhaust chambers are particularly useful for arc resistant cabinets containing electrical equipment, such as circuit breakers.
The exhaust chamber will preferably be located at the top of the arc resistant cabinet. A typical arc resistant cabinet includes a plurality of hinged flaps on the roof, thereby permitting high pressure, high temperature gases caused by an electrical arc inside the cabinet to exit the cabinet by pushing open these hinged flaps. The exhaust chamber includes a plurality of vertical walls surrounding that portion of the roof having these hinged flaps. One embodiment of the exhaust chamber includes horizontal shelves extending inward from the top of the vertical walls, thereby defining an opening in the center of the exhaust chamber""s top. An alternative embodiment includes a top extending across the entire exhaust channel, thereby completely enclosing the channel. In this second embodiment, a duct is connected to the exhaust chamber, leading away from areas where personnel are likely to be present. This duct could be extended in any direction, for example, vertically, to either side, to the front, or to the rear.
During normal operation of the electrical equipment within the cabinet, the hinged roof flaps will remain closed. If an electrical arc occurs, the high temperature, expanding gases apply upward pressure to the hinged flaps, thereby pushing the flaps upward. As the gases enter the exhaust chamber, they will have room to expand, thereby reducing their pressure. The gases will also have additional time to cool before exiting the chamber. If an open top expansion chamber is selected, the expanding gases will be directed by the vertical walls and horizontal shelves towards the center of the expansion chamber, where they will exit through the top of the chamber. If the enclosed expansion chamber is selected, the gases will expand into the chamber, and then continue expanding to enter the duct. Both embodiments will reduce the pressure of the gas, and permit sufficient time for cooling, to ensure the safety of personnel working around the cabinet.
It is therefore an aspect of the present invention to provide an expansion chamber for use with arc resistant cabinets.
It is another aspect of the present invention to provide an expansion chamber directing high temperature, expanding gases towards an opening in the chamber""s top, thereby providing sufficient time for cooling before these gases reach personnel.
It is a further aspect of the present invention to provide an enclosed expansion chamber, for directing high temperature, expanding gases into a duct.
These and other aspects of the present invention will become apparent through the following description and drawings.